PORTLAND, Maine — It was Friday “happy hour,” and on this sizzling-hot afternoon, the newest bar in the Old Port was already filling with thirsty patrons.

Despite the crowd’s obvious youth, head bartender and mixologist Tim Zabihaylo wasn’t asking them for proof of age. Why bother?

Zabihaylo was mixing drinks at Vena’s Fizz House, the only bar in the city — perhaps in the state — that serves soft drinks exclusively.

Vena’s, which opened July 10 at 345 Fore St., serves more than 35 varieties of all-natural, freshly made soda concoctions. They include pina colada, pomegranate limeade and even “Dim and Stormy,” which uses ginger beer and spiced tonic water to create a non-alcoholic version of a Dark and Stormy cocktail.

“This is a modern version of the old-fashioned soda parlor,” said Johanna Corman, who founded Vena’s with husband Steve and manages its operations. “We think we’ve found a niche.”

The business was inspired by Corman’s own taste.

“I drink a lot of seltzer, and I was always adding my own ingredients to it,” she said. “That’s kind of how things started.”

A Rosemont neighborhood resident, Corman said Vena’s is named after her great-grandmother, who was active during the late 1920s with the Woman’s Christian Temperance Union in Portland.

But the 22-seat watering hole caters to a different generation of teetotallers, including teens, families with small children, and adults looking for an alternative to the seemingly countless Old Port bars that serve alcoholic beverages.

On Friday, most of the crowd at Vena’s appeared to be years away from legally entering those establishments.

“It’s so hot. Let’s have something to drink before we go outside,” a girl said to another, while a woman herded two toddlers nearby.

Zabihaylo, one of 12 employees, was busy keeping glasses filled. That’s a familiar task for the Libbytown resident, who previously worked in conventional bars for nearly a decade.

“It’s nice to do something that’s not about alcohol, but where my experience and expertise aren’t lost,” he said.

The menu of drinks is constantly growing, as he experiments with new combinations of fruit, spices and mixers. Besides the lack of alcohol, the only requirement of his drinks is that they’re made with ingredients that are as fresh as possible. For example, instead of using a prepared mint syrup, Zabihaylo muddles mint leaves himself.

“We try to avoid anything that is premade, and use [ingredients] that are local,” he said. “Everything is craft-made; that’s the mixology mindset.”

Although the drink list isn’t like others in Portland, Vena’s resembles a conventional bar in many ways. The copper-clad counter was left behind by the former site occupant, Sebastian’s, a restaurant that opened [and closed] in 2012. Behind the counter, wooden shelves are filled with bottles and glassware. A flat-screen TV broadcasts from a wall.

Downstairs, where dining tables once stood, Corman sells cocktail glasses, shakers, coasters, mixers and other items for making both alcoholic and nonalcoholic potions. But most visitors gravitate to the bar.

“I tried to keep the bar atmosphere,” Corman said. “I wanted to create a gathering place where anyone could come.”

Asked if she worries about the influence of surrounding children and teens with that bar atmosphere, Corman said she is careful not to overdo the simulation. Her “mocktails” are served in mason jars, rather than traditional cocktail glasses. And Vena’s keeps early hours for a bar, closing at 9 p.m. Fridays and Saturdays and 8 p.m. on other nights.

“I thought about that risk, but I came to the conclusion that this could be a safe haven in the Old Port,” she said. “We’re just trying to be a place where everyone can come and have fun.”